This invention relates to an apparatus for heat sealing a plastic film cover over an open food container to produce an airtight package and particularly to improved heat sealing and trimming means.
Machines for heat sealing a plastic film cover or closure portion to an open plastic container are known in the art. Such machines are used to advantage in the preparation of pre-wrapped sandwiches which are to be dispensed from vending machines and it is imperative that the sealed container be completely airtight to avoid spoilage of the packaged merchandise.
The problems of adequately sealing plastic film to a high impact styrene container are considerable, primarily because of the sensitive heat and pressure control requirements. This has led, in many instances, to the use of special film, either of the pressure-sensitive type or the heat-activated, laminated type, which seal within a wide range of temperature and pressure or dwell time.
Another problem lies in the trimming or cutting of the plastic film, following heat sealing, in an efficient manner so that the seal is not impaired. The solution of this problem depends upon the satisfactory delivery of the film to the heat sealing station in a suitably tensioned condition. This has been achieved in the past only with relatively complicated, and therefore expensive, holding and feed devices.
Yet another problem lies in achieving correct clamping alignment of the mating heat sealing parts. The solution of this problem is particularly difficult when the sealing head is swingingly related to the container support and one approach is to provide close tolerances in the connections of the moving parts. Again, this is an expensive solution.
The present heat sealing apparatus solves the above and other problems in a manner not disclosed in the known prior art.